The invention relates to a turbocharger control and management system for maximizing the efficiency of a turbocharger and an internal combustion engine.
A turbocharger includes a compressor and a turbine. The turbine drives the compressor with exhaust energy created by the internal combustion engine. The engine exhaust drives a turbine wheel in the turbine of the turbocharger and is discharged through an exhaust system. The turbine wheel drives a shaft connected to a compressor wheel in the compressor which pressurizes intake air, previously at atmospheric pressure, and forces it typically through an intercooler and over a throttle valve and into an engine intake manifold. Controlling the output of the turbocharger to obtain desired engine operation has been a long standing problem. Too much output can create erratic engine performance and permanently damage engine components. Too little output causes engine hesitation, loss of power, and inefficient operation. Additionally, changes in atmospheric pressure, ambient temperature and engine speed affect the overall efficiency of the turbocharger which directly affects the performance, power output, and fuel economy of the engine.
Prior to the present invention, some turbocharger systems used a bypass valve connected to the output of the compressor to relieve excessive pressure. Typically, the bypass valve of these prior art systems sensed the differential pressure between the compressor discharge and intake manifold, i.e. the pressure difference across the throttle valve, and opened the bypass valve to vent pressure at a given threshold and remained open until the pressure fell below the threshold level. Other systems used a wastegate between the exhaust manifold discharge and the exhaust system to regulate the turbocharger by diverting engine exhaust energy from the turbine. The wastegate of this prior system was actuated by a compressor discharge pressure sensing type valve. Because these systems operated independently, and both were either opened or closed depending on the compressor discharge pressure, the turbocharger had a very limited efficient range of operation. The range was so limited that it was necessary to use different turbocharger hardware, i.e. turbine and compressor wheels, for varying altitudes of operation and engine configurations.
Since the turbocharger's compressor and turbine wheels are sized not only for altitude, but also to achieve a rated horsepower at a desired speed for each particular engine, the power and torque output of an engine would drop dramatically when the engine is run at less than the rated speed or at a different altitude because the pressure sensing valves were only dependant on compressor discharge pressure and would actuate regardless of engine speed. For example, an engine rated at 190 psi BMEP (braking mean effective pressure) at 1,000 rpm, would have trouble producing 190 psi BMEP at 700 rpm because of the reduced output of the turbocharger due to the falling speed and because of the mechanical pressure sensing and releasing valves previously used.
Typically, large industrial internal combustion engines operate for long periods and are capable of generating thousands of horsepower. These engines are designed to operate at 10% over rated load intermittently, and are used for generating electrical power, pumping natural gas and oil, powering large ships and off-shore well drilling operations, and so on. In such applications, it is desirable to produce maximum power and/or maintain maximum torque at reduced engine speeds. However, because previous turbocharger control systems were simply a function of the compressor discharge pressure, the mechanical valves would release pressure regardless of the engine's speed and therefore regardless of the engine's need. Under such circumstances, when the engine speed is reduced but the load is maintained, the engine requires near constant intake manifold pressure to maintain torque output. Under these conditions, it would be desirable to adjust the bypass valve to change total mass airflow and adjust the wastegate to direct more engine exhaust to the turbocharger in order to produce near constant intake manifold pressure such that the compressor operates more efficiently at these speed and load conditions.
The present invention provides a simple and effective method and system for maintaining engine torque output at lower than rated speeds and at varying ambient temperatures and barometric pressures by stabilizing the turbocharger output within a predetermined range of efficient operation.
Another object of the present invention is to provide an electronic turbocharger control system, including a wastegate and bypass valve, which eliminates the need for matching individual compressor and turbine wheels of a turbocharger for each particular engine configuration and application. This particular aspect of the invention allows a manufacturer to use one set of turbocharger hardware for various engine applications. For example, prior to the present invention, as many as 13 different turbocharger wheels would be required to adequately cover a 0-7,000 foot above sea level range of elevations. With the present invention, one set of turbocharger hardware can be used at all elevations in this desired range. Further economic advantage is gained not only by the low cost of the electronic control relative to the high cost of the compressor and turbine wheels, but also by the elimination of inventory and the need for custom wheels for special applications. Customer satisfaction may also be greatly improved by the elimination of long procurement leadtimes for replacement components.
Another aspect of the invention is to provide constant torque at varying engine speeds allowing an operator to obtain additional load at reduced engine speed for increased fuel economy.
Another aspect of the invention is to provide maximum power over a range of engine speeds while maintaining the turbocharger in its most efficient range of operation.
Yet another aspect of the invention is to provide a control system which maintains turbocharger efficiency within a desired range of pressure ratio versus mass air-flow rates.